FIG. 11 is a top view showing an example of a conventional wafer holding hand. FIG. 12 is a side view showing the wafer holding hand shown in FIG. 11. The wafer holding hand 200 holds a plurality of wafers W, and it is constituted so that fingers 201 are laminated. A vacuum hole 202 is provided in the center of each finger 201. Moreover, an air passage 203 for letting the air pass which is interconnected with the vacuum hole 202 is formed in the finger 201. Adsorption surface 204 of the finger 201 is finished smoothly so that the wafer W is easily adsorbed. The fingers 201 are laminated with spacers 205 in between and are fixed and supported by a frame 206. When the wafer W is placed on the finger 201 and air is sucked, a vacuum is created in the gap between the adsorption surface 204 and the wafer W, and both of them adsorb to each other. The adsorbed state between the wafer W and the adsorption surface 204 is released by stopping the suction of the air.
FIG. 13 is a top view showing another example of a conventional wafer holding hand. FIG. 14 is a side view of the wafer holding hand shown in FIG. 13. The wafer holding hand 300 has projections 302 along the shape of the wafer W on fingers 301. A slope 303 towards an inner side is provided on the projection 302. The wafer W is held by the projection 302 at the peripheral edge. A plurality of fingers 301 are laminated with spacers 304 in between and are fixed and supported by a frame 305. When the wafer W is placed on the finger 301, it moves along the slope 303 of the projection 302 to a predetermined position and held there.
However, in the wafer holding hand 200 shown in FIGS. 11 and 12, when the air suction is stopped, particles flow backward from the vacuum holes 202. Therefore, there is a possibility that a rear surface of the wafer W which contacts with the adsorption surface 204, and the wafer W on the down-stream side of the air current are contaminated. Moreover, there is a problem that the wafer W cannot be located properly on the finger 201.
In the wafer holding hand 300 shown in FIGS. 13 and 14, the wafer W is positioned by the projection 302, but since the wafer W is supported only by placing it on the projection 302, the wafer W can be transported only in the horizontal direction. Moreover, there is a problem that the transporting speed cannot be increased in order to prevent the wafer W from jumping out.
In addition, in the wafer holding hands 200 and 300, as a number of the fingers 201 and 301 and a number of the spacers 205 and 304 increase, a dimensional tolerance is accumulated. As a result, a tolerance of a distance between the bottommost finger and the topmost finger becomes larger, and thus mounting accuracy of the hand cannot be obtained.
Therefore, it is an object of the present invention to provide a wafer holding hand which is capable of preventing contamination of a wafer and simultaneously transporting the wafer freely, and capable of preventing drop of hand mounting accuracy.